1. Field of the Invention
The present invention relates to improvements in a thermo-hygrostatic refrigerator of the type using brine as cooling medium and more particularly, it relates to such a thermo-hygrostatic refrigerator wherein frequent start-stop operations of a compressor in the refrigerator may be avoided to thereby safe power consumption and enhance durability of moving parts. The present invention is also concerned with an improved thermo-hygrostatic refrigerator including means for rapid detection of unusual conditions such as interruption of brine circulation due to pump failure or other malfunctions, and shortage of brine circulation required for cooling the storage room.
2. Description of the prior Art
When perishable foods such as vegetables, fruit, meat and fish (hereinafter referred to as "food materials") are cold stored in a refrigerator for a long period of time, or when frozen food materials are gradually thawed, it is generally necessary to minimize changes in temperature within the refrigerator and control evaporation of moisture from the food materials. In order to meet the requirements, brine-cooled refrigerators, which use brine as cooling medium, have been put to practical use.
FIG. 7 shows an example of such refrigerators using brine as cooling medium. As shown therein, the refrigerator includes a cabinet 1 which defines a storage room 1a therein. A cooler 2 is located with the storage room 1a through which brine is circulated. A cooling unit section 3 is provided adjacent the storage room 1a including a refrigeration unit 10 which is composed of a compressor 4, a condenser 5, a drier 6, a capillary tube 7, an accumulator 8, an inlet pipe 9, etc. Reference numeral 11 designates a brine tank or container for storing brine 12 at a predetermined level. Disposed on the bottom of the brine tank 11 is an evaporator 13 which is connected in flow communication with the refrigeration unit 10 for forcibly cooling the brine 12.
The brine 12 cooled in the brine tank 11 is fed to the cooler 2 through an inlet pipe 17, a circulating pump 14, a discharge pipe 18 and a supply pipe 15 for cooling the air in the storage room 1a (hereinafter referred to as "internal air"). After cooling the internal air, the brine 12 is returned to the tank 11 through a feedback pipe 16. This cyclic operation is repeated to maintain the interior of the storage room 1a at a desired temperature.
Thus, the refrigerators using brine as cooling medium are capable of circulating a great amount of brine having large specific heat, as compared with ordinary refrigerators using freon gas as a cooling source and therefore, their cooling capacity may be made larger; the brine-cooled refrigerators are suitable to cool and store a great amount of food materials. In addition, temperature differences may be made less between the surface temperature of the cooler in the storage room 1a and the internal temperature and hence, moisture in the internal air may be restrained from frosting on the cooler surface, thereby maintaining the interior of the storage room at a high humidity.
In the above described thermo-hygrostatic refrigerator, the brine 12 stored in the brine tank 11 is cooled to a required temperature by the evaporator 13 connected to the refrigeration unit 10, and is supplied to the cooler 2 through the inlet pipe 17, the pump 14, the discharge pipe 18 and the supply pump 15. In the cooler 2, the brine 12 exchanges heat with the internal air and then returns to the brine tank 11. The temperature of the returning brine 12 is raised through the heat exchange and therefore, the temperature of the brine 12 in the tank 11 will also be increased. When the thus heated brine 12 is recirculated through the cooler 2 and is caused to exchange heat with the internal air, the temperature of the internal air will be gradually increased. Therefore, in order to maintain the temperature within a predetermined temperature range, the refrigeration unit 10 has to be reoperated, causing the evaporator 13 to cool the brine 12 in the tank 11 down to the required temperature range. At this point, when the brine 12 is cooled to the required temperature by the evaporator 13, the temperature of the cooler 2 becomes substantially equal to that of the circulating brine 12, thereby lowering the temperature of the internal air. As soon as the internal air is lowered to the required temperature, an internal temperature sensing device (not shown) will be actuated to stop the refrigeration unit 10.
When the refrigeration unit 10 is stopped, the operation of the evaporator 13 to cool the brine 12 will also be stopped. However, the internal air will continue to be cooled by the negative heat value stored in the brine 12 circulated by the pump 14 in motion.
It will be noted that the internal temperature is raised by various factors such as heat entering the storage room 1a through a heat insulating material 1b of the cabinet 1, heat entering the storage room 1a when doors are opened or closed, radiation from food materials stored in the storage room 1a, and radiation from a fan FM1 in the storage room 1a. When the internal temperature is raised, the temperature of the brine 12 will be gradually increased as the brine 12 exchanges heat with the internal air through the cooler 2. When the internal temperature exceeds an upper limit preset by the temperature sensing device, the refrigeration unit 10 will be reoperated by a signal from the sensing device causing the evaporator 13 to resume its cooling operation for the brine 12. In this way, the refrigeration unit 10 is operated when the internal temperature exceeds the upper set limit, and is stopped when the internal temperature falls below the lower set limit. By the repeated restart-stop operations, the internal temperature may be maintained within the predetermined temperature range.
As mentioned above, such thermo-hygrostatic refrigerators are designed so that the brine 12 in the tank 11 is circulated even when the refrigeration unit 10 is shut down, thereby causing the internal temperature to increase gradually by the use of negative heat value stored in the brine 12. However, if the amount of brine 12 stored in the tank 11 is small, the sum of heat entering the storage room may not be compensated by the negative heat value of the brine 12. This means that the interval is short in which the refrigeration unit 10, which has been shut down, may be reoperated, or in other words, the operation and stopping cycle of the refrigeration unit 10 is frequent, which may lead to shorter service life and higher failure rate of the compressor and other components. Further, every time the compressor 4 starts up, an excessive current flows thereinto, increasing power consumption.
In order to overcome these problems, it is possible to prolong the shutdown time of the refrigeration unit 10 by increasing the capacity of the brine tank 11, that is by increasing the amount of brine 12 to be stored in the tank 11, so that the negative heat value may be greater than the sum of entering heat and other heats. However, the use of a larger tank 11 renders the refrigerator itself larger, requiring a larger installation area and increasing manufacturing cost. In addition, the use of a larger tank 11 without increasing the external dimensions of the refrigerator tends to reduce the effective area of the storage room 1a, which in turn reduces the amount of food materials to be stored.
Further, the thermo-hygrostatic refrigerators are used generally for business purposes since they have a large cooling capacity, and in many cases a great deal of food materials are stored in the storage rooms. However, in case that the brine circulation is impossible or the brine amount is insufficient in the brine circulating pipelines for certain reasons such as, for example, failure of rotating parts of the pump and broken wire of the motor coils, the cooling operation in the storage room becomes impossible, which unusually increases the internal temperature. The stored food materials will then be deteriorated or rotten, causing great damages to the user.
In the event that cooling is not effected in the storage room, the prior art has proposed the use of a thermistor or the like which detects an unusual increase in the internal temperature and which actuates warning devices such as a lamp to warn nearby personnel of the unusual condition. However, such sensing means is likely to respond to a temperal temperature increase during defrosting operation and/or a temporal increase in the internal temperature due to frequent opening and closing of the doors, and it has sometimes issued erroneous warnings. For this reason, the sensitivity of such warning devices is set generally at a lower temperature, but in many cases, it may be rather late for the warning device to operate at the set point temperature. Specifically, when the warning device actually operates, the stored food materials may have already been deteriorated or rotten, suffering great damages.
The prior art has also proposed to electrically sense the presence of brine circulation by sensor elements disposed adjacent the brine circulation pipeline. However, the sensor, which is contiguous to the brine pipeline, tends to produce dew due to temperature differences from the ambient temperature. Under the influence of such moisture, malfunction and/or failure will result. Further, a larger space has been required to mount the sensor.